Diagnostic Utility of the Systemic Immune-inflammation Index for Acute Coronary Syndrome in Young Adults: A Prospective Case-control Study

Introduction: Acute Coronary Syndrome (ACS) in individuals under 40 years of age presents with distinct epidemiological characteristics, risk profiles and outcomes compared to older patients. Identifying cost-effective and reliable prognostic markers in this population is essential, particularly in resourcelimited settings. Composite inflammatory indices, such as the Systemic Immune-inflammation Index (SII), derived from platelet, neutrophil, and lymphocyte counts, has emerged as a promising biomarker in cardiovascular disease risk stratification. Aim: To evaluate the diagnostic utility of SII in differentiating young ACS patients from healthy controls, and to explore its prognostic value in predicting short-term Major Adverse Cardiac Events (MACE) within 30 days. Materials and Methods: The present prospective casecontrol study was conducted including 30 ACS patients aged <40 years and 30 age and sex-matched healthy controls, demographic data, clinical history, and laboratory parameters were collected. SII was calculated ((Platelet count*neutrophil count) / lymphocyte count). Statistical analyses included ROC curve analysis for diagnostic performance and other respective statistics based on the variable and normality. Statistical analyses were performed using Statistical Package for Social Sciences (SPSS) (v24.0). Results: The mean age of participants was 35.47±3.25 years, with 42 (70%) being male. The median SII was significantly higher in ACS patients compared to controls (p<0.001). ROC analysis demonstrated that SII (AUC 0.863, cutoff 613.875, sensitivity 96%, specificity 46%) for ACS diagnosis. Only two patients experienced MACE within 30 days, although the SII values were numerically higher, the difference was also statically significant (p=0.014). Conclusion: The SII, derived from routine complete blood count parameters, demonstrated strong diagnostic performance in identifying acute coronary syndrome among young adults. Given its simplicity and low cost, SII may serve as an adjunct diagnostic biomarker in early ACS detection, particularly in resource-limited settings. However, its prognostic value for short-term adverse outcomes remains exploratory and requires validation through larger, multicentric, and homogenous cohort studies.